The influenza A viruses (IAVs), particularly the highly pathogenic avian influenza (HPAI) H5N1 virus and the newly emerged avian-origin H7N9, continue to pose threats to public health and global economy because of their pandemic potential. This calls for the development of effective universal vaccines as the most prudent step against any emerging or re-emerging IAVs. The highly conserved extracellular domain of matrix protein 2 (M2e) and fusion peptide (FP) of hemagglutinin 2 (HA2) of influenza virus have been considered as important targets for universal influenza vaccines. Our preliminary studies have shown that a multiple antigenic peptide vaccine containing four M2e copies of H5N1 and a recombinant fusion protein linking three M2e molecules of H5N1 induced sufficient immune responses and cross-protection against divergent H5N1 strains and swine-origin 2009 H1N1 influenza virus. We also found that fusion of M2e with FP of H5N1 induced strong antibody responses against homologous and heterologous IAVs, including H5N1, H7N9, and H1N1, and maintained cross- protective immunity against divergent H5N1 strains, suggesting that linking the highly conserved epitopes in HA is a feasible approach to design universal influenza vaccines. Recently, the spore of Bacillus subtilis (B. subtilis), a Gram-positive, catalase-positiv bacterium, has been successfully applied as a powerful, noninvasive and heat-resistant mucosal vaccine delivery vehicle with high stability, long-term efficacy, and needle- and adjuvant-free properties. We thus hypothesize that B. subtilis spore-delivered universal influenza vaccines containing multiply-linked highly conserved sequences of M2e and FP of H5N1 and H7N9 can induce efficient mucosal immune responses and cross-protection against not only H5N1 and H7N9 but also other IAVs. We will carry out experiments for 1) design, express, and characterize B. subtilis spore-delivered M2e-FP-based mucosal universal influenza vaccine candidates, 2) detect immunogenicity and optimize immunization regimens of the B. subtilis spore-delivered M2e-FP-based mucosal universal influenza vaccine candidates, and 3) evaluate cross-protective immunity of a selected B. subtilis spore-delivered M2e-FP-based mucosal universal influenza vaccine candidate against challenges with representative strains of IAVs, including H5N1, H7N9, H1N1, and H3N2, in an animal model. The long-term goal of the proposed study is to develop a safe, effective and convenient B. subtilis spore-delivered M2e- FP-based mucosal universal influenza vaccine against a broad spectrum of IAVs, particularly H5N1 and H7N9. Such vaccine is expected to maintain strong heat-resistance, long-term stability, and cost-effective characteristics with capacity to induce improved efficacy through oral and intranasal delivery.